Succinic Acid Dihydrazide : a Convenient N , N-Double Block for the Synthesis of Symmetrical and non-Symmetrical Succinyl-bis [ 5-trifluoro ( chloro ) methyl-1 H-pyrazoles ]

Este trabalho apresenta a síntese regiosseletiva de séries de bis-2-pirazolinas e bis-1Hpirazóis succinil intercalados inéditas, denominadas 1,4-bis[5-(trifluormetil)-5-hidróxi-4,5diidro-1H-pirazol-1-il]butano-1,4-dionas (46-88%), o respectivo sistema desidratado (60-78%), 1-[5-(trifluormetil)-5-hidróxi-4,5-diidro-1H-pirazol-1-il]-4-oxabutano hidrazidas (52-81%) e 2-pyrazolinas derivadas não simétricas, como 1-[5-(trifluormetil)-5-hidróxi-4,5-diidro-1H-pirazol1-il)-4-(5-(triclorometil)-5-hidróxi-4,5-diidro-1H-pirazol-1-il]butano-1,4-dionas (75-91%). Todos os bis-pirazóis succinil substituídos foram obtidos a partir de reações de ciclocondensação de 4-alcóxi-1,1,1-trialo-3-alquen-2-onas 4-substituídas (4-substituinte = H, Me, fenil, 4-FC 6 H 4 , 4-ClC 6 H 4 , 4-OMeC 6 H 4 , 4-NO 2 C 6 H 4 , 1-naftil and 2-furil), com dihidrazida succínica, em etanol como solvente, sob condições reacionais convencionais controladas.

More recently, pyrazolylcarbohydrazides have been cited as new and promising antitumor drugs and have been synthesized and studied mostly as a potential lung cancer cell growth suppressant.In 2007, 16 a series of 1-arylmethyl-3-aryl-1H-pyrazole-5-carbohydrazide derivatives was synthesized and their effects on A549 cell growth and apoptosis were evaluated.The structureactivity relationships and prediction of lipophilicity of the compounds were also studied.Later, in 2008, 17 a new series of 1-(2′-hydroxy-3′-aroxypropyl)-3-aryl-1H-pyrazole-5carbohydrazide derivatives was synthesized.All of the 1-(2′-hydroxy-3′-aroxypropyl)-3-aryl-1H-pyrazole-5carbohydrazide derivatives inhibited the growth of A549 cells in dosage-and time-dependent manners.Typically, any compounds induced A549 and H460 cells to autophagy, but did not inhibit the growth of human umbilical vein endothelial cells (HUVEC).Thus, one can see that not only the bis-(pyrazolyl) spacer compounds, but also the pyrazolylcarbohydrazide intermediates are important.
On the other hand, it is well-known that the introduction of a trifluoromethyl group into heterocyclic compounds may have a significant influence on their biological and physical properties and the simple replacement of a hydrogen atom by a fluorine atom is a strategy widely used in drug development to alter biological functions.The resulting change in the electron distribution of a molecule following this replacement can alter the pK a , the dipole moments, and even the chemical reactivity and stability of neighboring functional groups.In terms of drug design, the employment of fluorinated molecules can be used to alter the rate of drug metabolism and thereby the production of a longer duration of action. 19he most convenient method to construct trifluoro and trichloromethylated heterocycles, including trihalomethyl substituted 2-pyrazolines and many pyrazoles, is to use fluorine-and chlorine-containing building blocks as starting reagents.][22][23] In this context and in an attempt to develop synthetic methods to obtain acyl spacer heterocycles and new fluorinated molecules, herein we report a practical and regioselective methodology for the preparation of a series of 1,4-bis(5-(trifluoromethyl)-5-hydroxy-4,5dihydro-1H-pyrazol-1-yl)butane-1,4-diones (2) and the respective dehydrated bis-pyrazole systems (3), new 1-(5-(trifluoromethyl)-5-hydroxy-4,5-dihydro-1H-pyrazol-1-yl)-4-oxobutane hydrazide intermediates (4) and the non-symmetrical 2-pyrazoline derivatives thereof as 1-(5-(trifluoromethyl)-5-hydroxy-4,5-dihydro-1H-pyrazol-1-yl)-4-(5-(trichloromethyl)-5-hydroxy-4,5-dihydro-1H-pyrazol-1-yl)butane-1,4-diones (5) from the cyclocondensation reactions of 4-substituted 1,1,1-trifluoro(chloro)alk-3-en-2-ones (1) with succinic acid dihydrazide in ethanol as solvent under conventional and controlled reaction conditions (Schemes 1 and 2).
In this work, we initially carried out the reaction of 4-methoxy-4-phenyl-1,1,1-trifluoro-3-alken-2-one (1c) with succinic acid dihydrazide in a 2:1 molar ratio, in ethanol as solvent at room temperature, however when monitored by TLC no reaction was observed.Subsequently, when the mixture was heated to reflux, after stirring for 6 h, TLC showed that the reaction proceeded smoothly and gave the product 2c in 79% yield (Scheme 1).The most satisfactory results for the synthesis of the other compounds 2 were obtained from the reaction condition described above and were isolated as stable solids by recrystallization from ethanol.
Subsequently, after a review of the literature and attempting to obtain aromatic pyrazoles for further biological assays, we chose thionyl chloride/ pyridine as the dehydration agent and report here the conditions required to accomplish the dehydration of two representative examples of compounds 2, which present a hydroxyl-and a trifluoromethyl-group, a phenyl (for 2c) or 4-fluorophenyl (for 2e) and a succinyl 2-pyrazoline attached directly to the C-5, C-3 and N-1 atom of each pyrazoline ring, respectively (Scheme 1).Because of the relative difficulty to perform the dehydration reaction, due to the presence of a trifluoromethyl substituent and the carbonyl function at positions 5 and 1 of these two succinyl-bispyrazolines, 2c and 2e were dehydrated to give the respective 3-aryl-substituted 1,4-bis(5-(trifluoromethyl)-1H-pyrazol-1-yl)butane-1,4-diones 3c and 3e in 78 and 60% yields, only by stirring the mixtures of 2c or 2e, thionyl chloride and pyridine at 80 ºC for about 1 h in benzene as solvent, according to similar procedures described in the literature. 24 o t i v a t e d b y t h e i m p o r t a n c e o f s o m e pyrazolylcarbohydrazides already described in the literature, 12,13 we attempted to synthesize some examples of new 1-(5-(trifluoromethyl)-5-hydroxy-4,5-dihydro-1Hpyrazol-1-yl)-4-oxobutane hydrazides (4).We investigated this reaction employing 4-substituted 4-methoxy-1,1,1trifluorobut-3-en-2-ones with two substituents with opposite electronic effects (4-methoxyphenyl and 4-nitrophenyl) and the neutral substituent 4-phenyl.Initially, we carried out the reaction of 4-methoxy-4phenyl-1,1,1-trifluorobut-3-en-2-one (1c) with succinic acid dihydrazide in a 1:1 molar ratio in ethanol as solvent at room temperature from 4 to 24 h, however when monitored by TLC no reaction was observed and the starting materials were recovered.Surprisingly, when the mixture was heated to 50-55 ºC, after stirring for 3 h, TLC showed that the reaction proceeded smoothly and gave product 4c in 81% yield (Scheme 2).The most satisfactory results for the synthesis of the other compounds 4 were obtained from the reaction condition described above and the compounds were isolated as stable white powders after the reaction time by simple filtration under reduced pressure in 52-81% yields.
Finally, aiming to obtain examples of non-symmetrical succinyl spacer bis-pyrazoles, the reaction of 1-(3-phenyl-5-(trifluoromethyl)-5-hydroxy-4,5-dihydro-1H-pyrazol-1yl)-4-oxobutane hydrazides 4c with two trichlorometylated vinyl ketones (4-methoxy-1,1,1-trichloropent-3-en-2-one and 4-methoxy-4-phenyl-1,1,1-trichlorobut-3-en-2-one) was performed.In these cases, the desired products 5b and 5c were isolated in 91 and 75% yields, respectively, showing an interesting and promising employment of pyrazolyl substituted succinic acid hydrazides such as 4 (Scheme 2).Compounds 5 were obtained when the reactions of pure 4c and 4-methoxy-1,1,1-trichloroalk-3en-2-ones were carried out in a molar ratio of 1:1 at 50 ºC for about 16 h also in ethanol as solvent.A complex mixture of products was obtained when the reactions were carried out under refluxing ethanol for 1 to 2 h.The structures of 1,4-bis[5-(trifluoromethyl)-5hydroxy-4,5-dihydro-1H-pyrazol-1-yl]butane-1,4-diones (2a-f, 2h-i) were deduced from NMR experiments and by comparison with NMR data of other 2-pyrazolines formerly synthesized in our laboratory. 18,22,23Compounds 2 showed the 1 H NMR chemical shifts in DMSO-d 6 of the hydroxy protons in the range of d 8.04 ppm and the four methylene protons (H4) are shown as a typical AB system as two doublets, in which, one of them is on average at d 3.79 and the other at d 3.44 ppm, with a geminal coupling constant of 19-20 Hz.Due to the symmetry of compounds 2, the four ethylene protons (succinyl moiety) appeared as one singlet peak on average at 3.06 ppm.The 13 C{ 1 H}NMR spectra exhibited only one set of peaks, despite the fact that two stereogenic carbons are present in each molecule.The succinyl derivatives 2 also presented the typical 13  For the pyrazolyl-succinic acid hydrazides (4), the OH, NH and NH 2 groups showed 1 H NMR chemical shifts in DMSO-d 6 in the range of d 7.97 ppm, d 8.97 ppm and d 4.15 ppm, respectively.Now, due to the non-symmetry of compounds 4, the four methylene protons of the succinyl moiety appeared as broad peaks on average at 3.07 and 2.24 ppm.As expected, the 13 C{ 1 H} NMR spectra exhibited only one peak for each carbon of the pyrazoline ring and the hydrazinosuccinyl moiety.
The unambiguous 1 H and 13 C NMR chemical shift assignments of non-symmetrical 1-[5-(trifluoromethyl)-5-hydroxy-4,5-dihydro-1H-pyrazol-1-yl]-4-[5-(trichloromethyl)-5-hydroxy-4,5-dihydro-1H-pyrazol-1-yl]butane-1,4-diones (5b-c), in DMSO-d 6 as solvent, were made by comparison with NMR data of other trifluoro(chloro)methyl substituted 2-pyrazolines formerly obtained in our laboratory. 18,22,23In contrast to compounds 2, molecules 5 showed two sets of NMR signals.The chemical shifts of the four diasterotopic methylene protons (H4) appeared, as typical AB systems, as four doublets with a geminal coupling constant on average at 19 Hz.The hydroxy protons, as two singlets, are shown in the 1 H NMR spectra in the range of d 7.72-8.05and the four methylene protons of the succinyl moiety appeared as broad peaks on average at 3.09 ppm and 2.97 ppm.Compounds 5 also presented the typical 13 C{ 1 H}NMR spectra where the chemical shifts for non-symmetrical structures showed separate signals for each pyrazoline ring carbons.Also, due to the non-symmetry of 5b-c, the two carbonyl carbon methylene groups of the succinyl moiety appeared as four peaks which is consistent with NMR chemical shift assignments when compared with compounds 2 and literature data for trichloromethyl substituted 2-pyrazolines. 23

General procedures
Unless otherwise indicated all common reagents and solvents were used from commercial suppliers without further purification.All melting points were determined using open capillaries on an Electrothermal Mel-Temp 3.0 apparatus and are uncorrected. 1H and 13 C NMR spectra were acquired on a Bruker DPX 200 spectrometer ( 1 H at 200.13 MHz and 13 C at 50.32 MHz), 5 mm sample tubes, 298 K, digital resolution ± 0.01 ppm, in DMSO-d 6 for 2-5 using TMS as internal reference and all coupling constants (J) are given in Hertz (Hz).The CHN elemental analyses were performed on a Perkin-Elmer 2400 CHN elemental analyzer (São Paulo University, USP/Brazil).

General procedure
A solution of bis-pyrazoline butane-1,4-diones (2c, 2f) (2.8 mmol) and pyridine (33.8 mmol, 3 mL) in 50 mL of benzene was cooled to 0 ºC and thionyl chloride (16.8 mmol, 1.22 mL) diluted in 25 mL of benzene was added dropwise over 10 min.The solution was stirred for an additional 30 min, during which time the temperature was allowed to rise to 20 ºC.The mixture was then heated under reflux (bath temperature 80 ºC) for 1 h and then filtered to remove the pyridine hydrochloride at room temperature.The solution was extracted twice with benzene (2 × 50 mL) and dried over sodium sulfate.Evaporation of the solvent under reduced pressure by rotatory evaporator left 3c, 3f as solid products which were purified by recrystallization from ethanol.

General procedure
To an ice-cold stirred mixture of 4-substituted 4-alkoxy-1,1,1-trifluoro-3-alken-2-ones 1c-d (10 mmol) diluted in ethanol (15 mL) another mixture of succinic acid dihydrazide (10 mmol) and ethanol (10 mL) was added at room temperature.The resulting new mixture was stirred for 4 h at 50 o C.After the reaction time the solvent was evaporated to half by rotatory evaporator under reduced pressure and after cooling (≤ 8 ºC) for 1-2 days the compounds 4c-d, 4g were obtained pure directly by filtration, washed with cold ethanol and dried under vacuum apparatus.
C NMR chemical shifts of the both pyrazoline rings at d 149.8 ppm (C3) and d 45.2 ppm (C4).Due to the presence of the CF 3 group, both C5 carbons presented a characteristic quartet at d 90.3 ppm with 2 J CF 33 Hz.Also, both CF 3 groups showed a typical quartet at d 123.4 ppm with 1 J CF 285 Hz and the two carbonyl and ethylene carbons showed NMR signals in the range of d 170.1 ppm and 29.3 ppm, respectively.All the signals are consistent with 1 H and 13 C NMR chemical shifts of the pyrazoline and the succinyl moiety for this symmetrical system.The dehydrated compounds 3c and 3f, being symmetrical systems, presented one set of signals in both 1 H and 13 C NMR spectra and, in comparison with 2c and 2f showed typical chemical shifts of the pyrazole ring for both H-4 on average at 7.5 ppm as singlet peaks.The 13 C{ 1 H} NMR spectra exhibited chemical shifts, in DMSO-d 6 , for both pyrazole ring carbons on average at 152.6 (C3), 111.7 (C4), 134.1 (C5, 2 J CF 41) and 119.1 ppm (CF 3 , 1 J CF 268).Both carbonyl and ethylene carbons showed signals in the range of d 169.8 ppm and 29.5 ppm, respectively.